— A potent cold front swept across the San Francisco Bay Area early Tuesday, producing thunderstorms with lightning, heavy rain and scattered small hail across the North Bay and northern Contra Costa County. High-resolution models showed a concentrated band of intense showers moving through San Francisco, Oakland and San Jose in the late morning; storms were expected to become more scattered by afternoon but to persist in spots until after sunset. Snow fell on several peaks — including Mount St. Helena, Cobb Mountain and Mount Hamilton — and flakes were visible on Mt. Diablo cameras. Officials issued winter and cold-weather alerts for mountain zones and lowland cold advisories for parts of the region as overnight lows plunged into the upper 20s and 30s.
Key takeaways
- The National Weather Service and its Storm Prediction Center placed much of California in a general thunderstorm risk on Feb 17, 2026, with small hail and gusty winds listed as primary hazards.
- Snow was reported on Mount St. Helena, Cobb Mountain and Mount Hamilton; cameras atop Mt. Diablo recorded snowflakes. Snow is expected mainly above 2,500 feet.
- Winter weather advisories remain in effect through Wednesday for the Santa Lucia range and mountains of San Benito and eastern Santa Clara counties; an extreme cold warning begins at midnight for parts of Monterey and San Benito counties.
- Forecast overnight lows will fall into the upper 20s to 30s in some valleys and mountain-adjacent areas — potentially the coldest night since February 2023 for parts of the region.
- High-resolution models showed intense shower bands moving through San Francisco, Oakland and San Jose in the late morning, with showers moving faster than 50 mph in some places and wind gusts commonly 30–40 mph, locally exceeding 50 mph.
- Hail can survive the fall to reach near sea level and has previously coated streets in San Francisco and Oakland; urban flooding is possible where heavy showers stall.
- Several localized impacts were reported, including a handful of power outages (including at Stanford University) and ferry cancellations or service disruptions in San Francisco Bay.
Background
The system arriving Feb 17 is rooted in frigid air spilling south from the Gulf of Alaska. As that cold air moved over comparatively warmer Pacific surface waters, it strengthened upward motion in the lower atmosphere — a setup that supports embedded thunderstorms even along a normally stable California coast. The Bay Area’s persistent marine layer typically limits thunderstorm intensity and hail formation, but forecasts indicated this air mass was the coldest in roughly three years, thin enough to erode the marine layer and allow stronger convective updrafts.
Hail in the Bay Area is uncommon because hailstones usually melt while passing through the warm, moist boundary layer over the ocean. However, strong updrafts can loft ice high enough that hail survives long enough to fall to lower elevations — occasionally to sea level. The region has prior examples of significant hail events that briefly turned neighborhoods white, creating slick conditions and localized property damage. Emergency managers and transit operators track these storms closely because they combine lightning, heavy downpours and strong gusts that affect power, ferries and road travel.
Main event
Early Tuesday morning, thunderstorms with frequent lightning struck the North Bay and northern Contra Costa County as the cold front pushed through. Meteorological radar and high-resolution convection-allowing models showed a narrow, intense band of showers sliding from northwest to southeast across the urban corridor, producing high rainfall rates and embedded small hail. Those bands were predicted to cross San Francisco, Oakland and San Jose during the late morning window before storms began to scatter in the afternoon.
Snow reports arrived from higher terrain: a few inches appeared to have accumulated on Mount St. Helena and Cobb Mountain, with similar reports on Mount Hamilton. Cameras on Mt. Diablo captured occasional flakes, though precipitation there was expected to be light and transient. Authorities kept a winter weather advisory in effect through Wednesday for the Santa Lucia range and for mountains in San Benito and eastern Santa Clara counties; an extreme cold warning was scheduled to begin at midnight for the Santa Lucias and interior sections of Monterey and San Benito counties.
Wind was a notable hazard alongside precipitation. Forecast guidance indicated widespread gusts of 30–40 mph, with thunderstorms capable of producing localized gusts above 50 mph. Showers embedded in the convective band were moving rapidly — in some instances faster than 50 mph — which could make blue skies switch to intense downpours with little lead time. Where heavy showers lingered, the combination of high rainfall rates and urban drainage limitations raised the prospect of flash urban flooding.
Analysis & implications
Meteorologically, the event illustrates how strong cold-air intrusions can temporarily override the Bay Area’s usual marine moderation. The cold pocket aloft produced by the Gulf of Alaska air mass increased lapse rates and buoyancy in the lower troposphere, enabling thunderstorm development over coastal and near-coastal zones that normally remain capped. That dynamic explains how small hail reached lower elevations even as snow stayed confined mainly to peaks above 2,500 feet.
From an infrastructure perspective, the mix of lightning, hail and high winds amplifies short-term risks to power and transit. Gusts above 50 mph can topple weak trees and branches, and small hail can create slick road surfaces and reduce tire grip. Ferry operators and road agencies may need to stage crews for debris clearing and localized pumping where drains become overwhelmed. The handful of power outages reported — including at Stanford University — underscores how quickly impacts can materialize in urbanized corridors.
Economically and socially, the timing of the cold snap matters. Overnight lows in the upper 20s to 30s can stress vulnerable outdoor workers, shelter systems and agriculture in low-lying valleys and coastal plains. While the most intense convective activity was forecast to taper after sunset, the extreme-cold window that followed could increase freeze risk for late-season crops and infrastructure exposed to sustained subfreezing temperatures. Longer-term, events like this raise questions about emergency preparedness and how well local systems can handle compound hazards (flooding plus wind plus cold).
Comparison & data
| Zone | Expected precipitation type | Elevation threshold | Primary hazards |
|---|---|---|---|
| Mount St. Helena, Cobb Mountain | Snow (a few inches) | >2,500 ft | Snow accumulation, slick access roads |
| Mount Hamilton, Mt. Diablo cameras | Snow/snow flurries | >2,500 ft (light) | Short-lived flurries, visibility reductions |
| San Francisco/Oakland/San Jose | Heavy rain, small hail | Sea level possible for hail | Urban flooding, slick roads, lightning, gusty winds |
| Santa Lucia range | Snow/higher-elevation wintry mix | >2,500 ft | Winter travel impacts; extreme cold overnight |
These comparisons show that while wintry precipitation was concentrated at higher elevations, convective hail and heavy rain posed the larger near-sea-level threat. Models and observed reports placed the most intense convective rainfall rates in urban corridors during the late morning of Feb 17; advisory and warning products targeted mountain travel and interior valleys where overnight cold would be most severe.
Reactions & quotes
“Trends will continue to be monitored regarding potential for a brief tornado threat associated with this strong system.”
National Weather Service Storm Prediction Center (official)
The SPC highlighted the low but non-zero potential for transient rotation within strong convective cells, prompting continued situational awareness for severe-weather crews.
“Small hail and gusty winds are the main threat across much of California today.”
National Weather Service forecast office (official)
Local forecast offices emphasized hail and wind as primary hazards and reiterated guidance to slow for hail, avoid flooded roadways and expect rapid changes in conditions.
Unconfirmed
- Exact snowfall totals on some peaks remain preliminary until ground-verified measurements are reported by local agencies.
- Reports of isolated short-lived funnel clouds and waterspouts are being evaluated; confirmations require eyewitness or radar-track validation.
- The full extent and duration of localized power outages and ferry-service disruptions are still being compiled by operators and utilities.
Bottom line
The Bay Area saw an uncommon mix of convective storms, hail and mountain snow on Feb 17, 2026, driven by an unusually cold air mass from the Gulf of Alaska. While the most intense late-morning convective band was expected to break up and become more scattered by afternoon, pockets of heavy rain, hail and gusty winds could linger until after sunset, and a cold night followed with warning-level impacts in mountain and interior counties.
Residents should plan for rapid changes in conditions: slow down or pause travel during hail or heavy downpours, prepare for gusty winds and possible short outages, and heed winter and cold-weather advisories for higher terrain and vulnerable lowland pockets. Officials and providers will continue monitoring into Wednesday as temperatures normalize gradually, but the overnight cold and residual showers warrant caution through the advisory period.
Sources
- San Francisco Chronicle — news reporting and local observations
- Storm Prediction Center (SPC) / National Weather Service — official convective risk and guidance
- National Weather Service (NWS) — local forecasts, watches and warnings